The present invention relates to a four-blade rotor, especially for helicopters in which the rotor blades are arranged in pairs. The blades of a pair are located diametrically opposite each other and secured to the rotor head for permitting a blade angle adjustment. Between the blade roots of the blades forming a pair, coupling means are located in the form of a belt, for example, which is tension resistant but torsionally yielding. One coupling means such as a belt extends in a vertical plane and the other torsionally yielding coupling extends in a horizontal plane, whereby the latter passes through the vertical, torsionally yielding coupling means.
German Patent No. 1,531,359 describes a rotor of the type just mentioned wherein the torsionally yielding coupling or connection of the respective rotor blade pair passes freely through the rotor head center in such a manner that cyclic blade angle adjustments do not cause any twisting of the torsionally yielding coupling. Thus, the torsion loading of the coupling is substantially determined only by the collective blade angle adjustment. Incidentally, the cyclic blade angle adjustment involves tilting the two rotor blades arranged diametrically opposite each other in the same direction and to the same extent.
However, practical experience has shown that is it not possible to do without a central holding of the rotor blade pair at the rotor head due to unbalances and vibrations in the direction of the rotor blade. Thus, the just described rotor did not attain any practical significance. It is customary to make the torsionally yielding couplings in the form of laminated bundles of fiber reinforced materials. These couplings interconnect a respective rotor blade root with a central body arranged coaxially to the rotational axis of the rotor head as described in German Pat. No. 2,150,741. In this type of arrangement it is not possible to obviate the fact that for each angular movement of the individual rotor blade a twisting of the corresponding laminate bundle takes place which twisting is effective all the way to the central body. The couplings form elongated loops.